Optical temperature sensing in Er³⁺-Yb³⁺ codoped CaWO₄ and the laser induced heating effect on the luminescence intensity saturation

CaWO₄ phosphors doping with different Er³⁺ and Yb³⁺ ion concentrations were synthetized through high temperature solid-state reaction technique. Excited by 980 nm laser, the influence of rare earth dopant concentration on the thermometry behavior of Er³⁺ green upconversion emissions was discussed via the fluorescence intensity ratio method. Superior temperature sensing ability could be achieved in CaWO₄: 0.1 mol% Er³⁺-3 mol% Yb³⁺, the maximum sensitivity of which is about 1.05 × 10⁻² K⁻¹ at 439 K. Meanwhile, the pumping laser induced thermal effect on the saturation of upconversion emission intensity has been preliminarily studied. The temperature of the irradiation spot on sample caused by the exposure of excitation laser is observed to be greatly enhanced as the pumping power increased. Based on the steady-state rate equations and the temperature dependence of luminescence decay curves, theoretical calculations have been performed. The results confirm that the laser induced heating effect plays an important role in the luminescence intensity saturation phenomenon. - Highlights: • The effect of Er³⁺ and Yb³⁺ doping content on the thermometry behavior is studied. • A maximum sensitivity of 1.05 × 10⁻² K⁻¹ at 439 K is achieved. • Laser induced temperature increase at laser spot on sample is studied based on FIR. • Laser thermal effect actually contributes to the luminescence intensity saturation.